This invention relates to polyurethane/urea/thiourea latexes prepared from a urethane/urea/thiourea prepolymer.
Polyurethane/urea/thiourea latexes are generally prepared by chain extending the reaction product of an organic diisocyanate and an organic compound having two active hydrogen atoms such as polyalkylene ether glycols, poly(alkylene ether-alkylene thioether) glycols, alkyd resins, polyesters and polyester amides. The diisocyanate is used in stoichiometric excess so that the reaction product, also referred to as a polyurethane/urea/thiourea prepolymer, is isocyanate terminated. The prepolymer is typically prepared in the presence of a solvent. Examples of polyurethane prepolymer preparations are described in U.S. Pat. Nos. 3,178,310; 3,919,173; 4,442,259; 4,444,976; and 4,742,095, inter alia.
U.S. Pat. No. 3,294,724 discloses the preparation of a film-forming urethane latex by chain extending the isocyanate-terminated prepolymer with a piperazine compound. First, the prepolymer is prepared by reacting a polyalkylene ether glycol with a diisocyanate. A prepolymer emulsion is then formed, whereupon a piperazine compound dissolved in cold water is added to the emulsion with stirring to form a stable chain-extended latex. A solvent such as toluene or cyclohexanone is used either in the step to form the prepolymer or in the chain extension step.
The solids content of a typical polyurethane latex tends to be in the range of about 30 to 40 weight percent. For example, U.S. Pat. No. 4,742,095 describes the preparation of a polyurethane latex having a solids content of as high as 41 weight percent. To minimize transport costs and drying times, it is desirable to prepare a polyurethane latex that maximizes solids content without having to resort to additional concentration means such as evaporation of water.
It would be advantageous to prepare a polyurethane/urea/thiourea latex in the substantial absence of any ancillary organic solvents. It would be further advantageous to prepare such a latex having a high solids content, with controlled particle size, and a narrow particle size distribution. Finally, it would be desirable to prepare a polyurethane latex from less expensive raw materials such as aromatic diisocyanates. Such a latex would be particularly useful as a carpet backing.